There are three general types of two cycle induction. The most simple type of air intake induction is called a piston port engine. This type of two stroke engine has holes cut through the cylinder walls in specific areas. The second type of induction, and the most popular type, is reed block induction. This consists of multiple reed petals that allow air into the crankcase and keep it trapped there. The third type of two stroke induction is generally used in rotax two cylinder engines is the rotary valve engine. It does slightly better than reed engine because there is no restriction from reed petals. The rotary valve rotates past the crankcase intake port at a specific time to allow air through then seal the air into the crankcase.

2 Stroke engine repair can be accomplished once the severity of the problem or damage is assesed. As with all engines, they require two basic things to operate. First all engines require fuel. There are a few ways to check if the engine is getting fuel. Remove the spark plug and see if they are wet. If the spark plug is not wet, you can remove the float bowl to see if fuel is being delivered to it. If there is no fuel you can check the needle and seat of the carburetor, or the fuel pump. You can generally repair a sticking needle simply by moving the needle manually. If the 2 stroke engine is fuel injected you will need a fuel pressure gauge and will then need to attach it to the fuel rail. Check that the specified pressure is being reached. If not, the fuel pump is probably faulty. The next important thing to check is that the engine is producing spark.

Snowmobile fuel pump problems can be diagnosed. A vacuum fuel pump is used on snowmobiles with carburetors. The first thing to look at is the vacuum line that will run to the crankcase. If this hose has any cracks, leaks or is not clamped tightly on to the crankcase fitting, it will not pump fuel. If the fuel pump still wont work, mark where the lines come from and make a line down the side of the pump. Disassemble the pump carefully and look at the diaphragms for cracks. Also inspect for blockage of any of the cavities or passages within the fuel pump. You can also spin the engine over to make sure the crankcase fitting is not blocked. This fitting will produce vacuum and pressure so don’t be alarmed. If you can’t find any problems rebuild or replace the pump. Fuel injected snowmobiles will use an electric fuel pump. First check to see that there is voltage coming to the fuel pump.

A rotary valve engine is always a two stroke engine. Most rotary valve engines are rotax engines. Although other rotary engines such as suzuki and kawasaki have been made. Rotax engines are used in snowmobiles, jet-skis and motorcycles and aircraft engines. A rotary valve refers to the intake of a two stroke engine. There are three types of intake designs for two stroke engines. Simplistic two strokes are piston port, meaning that the piston movement past the port controls the incoming air timing. The piston port engine doesn’t do a very good job of keeping the airflow to stay in the engine. The air can simply travel back out of the engine. The most popular intake air induction is the reed port engine. It uses reed petals to allow the intake air in the engine and traps it there. The tension of the reed petals can change with the use of different petals and can provide some power improvement at certain rpm ranges. A rotary valve engine has the best intake air control.

Snowmobile engines are generally two strokes except for a few new four strokes. Repair and troubleshooting is similar to any other vehicle. First you want to identify if it is a fuel or ignition problem. Remove the spark plugs and look to see if they are wet or dry. Do they both look the same or are they different? If different then one cylinder’s carb or ignition may have a problem. A wet spark plug could be many things. Take the spark plugs, dry them off with a clean rag and place them back into the plug wire. Lay the spark plugs on a metal part of the engine and spin the engine(try to start) Look at the plug gap as you spin the engine over, do they all spark descent? If some of the sparks look weak you could have an ignition problem. Hopefully the plug is fouled out and just needs to be replaced, try that first. If weak spark remains, check that the ground wire for the ignition coil or system is good. Worst case you could have a bad charging coil or bad wires shorting out somewhere.

Piston rings are a very crucial part of a two stroke engine. If the rings stick they can be freed up, assuming there was no cylinder damage involved. If the cylinder is smeared vertically with aluminum it is damaged. The cylinder will need to be cleaned up with muriatic acid then honed out until the lines are gone. If too much honing is required the piston may not be large enough anymore and may need to be replaced. If the rings are only stuck then they need to be removed. If they are stuck hard you can try to soak the piston in diesel fuel or pb blaster. The ring may need to be pryed out carefully.